4He, 3He, and 3He-4He dilution refrigerator Physics 590 B, Spring 2014 4He, 3He, and 3He-4He dilution refrigerator Instrument Gas handling system Still pumping line Magnet power supply Dil fridge Dump (mixture storage) Pump room 3He pumping Oxford 14 T cryostat LN 2 trap LHe Dewar LN 2 Dewar Vacuum pump Turbo pump Rotary pump Computer-data acquisition Typical dil-fridge room 4He, 3He, and 3He-4He dilution refrigerator Instrument Gas handling system Still pumping line Dil fridge Magnet powersupply Dump (mixture storage) Pump room 3He pumping Oxford 14 T cryostat LN 2 trap LHe Dewar LN 2 Dewar Vacuum pump Turbo pump Rotary pump Computer data acquisition Typical dil-fridge room DON’T 4He, 3He, and 3He-4He dilution refrigerator measurements Instrument Gas handling system Still pumping line March 10-14 March 3-7 Dil fridge Magnet powersupply Dump (mixture storage) Pump room 3HeKaminski pumping Oxford 14 T cryostat LN 2 trap LHecryogens Dewar cryogensLN 2 Dewar MarchVacuum 3-7 pump Turbo pump RotaryKaminski pump Computer data acquisition How to cool below 4 K 4He, 3He, and 3He-4He dilution refrigerator 4He Phase diagram Cryostat Cooling power Pressure, thermometer 3He Isotopes of Helium Phase diagram Cooling power Refrigerator- closed system with charcoal, measurements in liquid Thermometer 3He-4He Mixture Phase diagram of mixture Properties of mixture Cooling power of mixture Operation Cryogen free system Thermometer Very nice reference book: Matter and Methods at Low Temperatures, 2 nd Edition, F.Pobell Cryogenic systems 4He Phase Diagram Critical point 5.19 K Triple point ~ 2.17 K at 1 atm Boiling point 4.222 K (0.22746 MPa) • 4He has no spin, Boson • No solid phase (1 atm) due to weak van der Waals inter-atomic interactions, large quantum mechanical-zero-point energy due to small mass (high kinetic energy and low Potential energy), Bose-Einstein condensate instead of a solid • Helium-4 : triple point involving two different fluid phase. The λ(lamda)-point is the temperature below which normal fluid helium transition to superfluid helium. 4He Cryostat 4He pumping Sample holder Sample space Vacuum sapce LN 2 LHe Base temperature 4.2 K at 1 atm Cool below 4.2 K Reduce pressure – pumping cryostat down to ~ 1K Reality! 1.5 ~ 2 K Sample Cooling power is proportional to vapor pressure. space Cryostat design magnetic field – March 10-14 4He Cryostat with 1 K pot 1K pot pumping Needle valve Sample space Capillary flow (impedances) Cool down sample stage by 1 K pot or use VTI Save Helium! Save money! Efficient! 1K pot Difficult to cool down below 1.5 K Sample should be called 2 K pot? space 4He Cryostat with 1 K pot 1K pot pumping Needle valve Sample space reach ~0.9 K and sample in liquid Small volume with low impedance: easy to reach low pressure He gas Sample space pumping below 1 K Small He bath/VTI pumping < 2K 1K pot Liquid He Sample inside liquid sample High vacuum charcoal Cooling power of evaporative cooling dP S − S L LP = gas liq ~ = dT V −V TV RT 2 gas liq gas latent heat of 3He and 4He V >> V L ~ TdS Assuming gas liq and using Latent heat L ~ independent of temperature 4He dP L dT = (J/mol) P R T 2 L L 3 P ∝ − He exp( ) Latent heat RT Cooling power: proportional to vapor pressure and exponentially small with temperature Temperature (K) Pressure Pressure ranges of vacuum -details March 3-7 low pressure, vacuum generation and gauge (Kaminski) Torr Vacuum gauge pump Atmospheric 760 Low vacuum 25 ~ 1 X 10 -3 Pirani gauge (0.5 ~ 10 -4 Torr) Rotary pump High vacuum 1 X 10 -3 ~ 1 X 10 -9 Ionization gauge (10 -3 ~ 10 -10 Torr) Turbo pump, diffusion pump, Penning gauge (10 -3 ~ 10 -13 Torr) cryopump (charcoal) -9 -12 Ultra high vacuum 1 X 10 ~ 1 X 10 Inverted magnetrons (~ 1 X 10 -12 ) Outer space 1 X 10 -6 < 3 X 10 -17 U-Tube Manometer Perfect vacuum 0 Bourdon Tube Capacitance Manometer Themocouple McLeod 1 atm Schulz-Phelps IG = 1.01325 X 10 5 Pascal (Pa) Bayert-Alpert IG Pirani gauge = 1.01325 Bar (bar) Cold Cathode IG Penning gauge = 760 Torr (mm Hg ) Mass Spectrometer (RGA) = 14.69595 Pound per square inch (psi) 10 -13 10 -11 10 -9 10 -7 10 -5 10 -3 10 -1 10 1 10 3 Pressure in Torr 4He thermometer January 22-24 measuring temperature (Prozorov) Cernox™ sensors can be used from 100 mK to 420 K with good sensitivity over the whole range. They have a low magnetoresistance, and are the best choice for applications with magnetic fields up to 30 T (for temperatures greater than 2 K). Cernox™ are resistant to ionizing radiation, and are available in robust mounting packages and probes. Because of their versatility, they are used in a wide variety of cryogenic applications, such as particle accelerators, space satellites, MRI systems, cryogenic systems, and research science. From Lakeshore.com CX-1050 -SD/BC X00000 : good sensitivity and stability Response time 1.5ms CX-1050 for 4He CX-1030 for 3He Response time 15ms Time related measurements such as AC heat capacity Consider response time BC: 1.5 ms at 4.2 K, 50 ms at 77 K, 135 ms at 273 K SD: 15 ms at 4.2 K, 0.25 s at 77 K, 0.8 s at 273 K I2R AA: 0.4 s at 4.2 K, 2 s at 77 K, 1.0 s at 273 K Low current or voltage (~2mV): Joule heating Isotopes of Helium 3He 4He Parent isotopes 3H (beta decay of tritium) Neutron 1 2 proton 2 2 Isotope (atomic) mass (m a/u) 3.016 4.002 Nuclear spin (I) 1/2 0 Magnetic Moment (µ/µN) -2.127 0 Half life Stable stable Natural abundance (atom %) on Earth 0.000137 99.99986 Boiling point at 1atm 3.19 K 4.23 K Critical point 3.35 K 5.19 K (0.22746 MPa) Triple point 2.177 K (5.043 kPa) Density of liquid at boiling point 0.059 g/mol 0.12473 g/mol Latent heat of vaporization 0.26 kJ/mol 0.0829 kJ/mol Molar heat capacity 5/2 R = 20.768 J/mol Other isotopes, He-5, He-6 He-7 … extremely short half-life The shortest-lived heavy helium isotope is He-5 with a half-life of 7.6×10−22 s. He-6 decays by emitting a beta particle and has a half-life of 0.8 second. He-7 also emits a beta particle as well as a gamma ray. He-7 and He-8 are created in certain nuclear reactions. He-6 and He-8 are known to exhibit a nuclear halo. C. A. Hampel (1968). The Encyclopedia of the Chemical Elements. pp. 256–268. 3He Phase Diagram Critical point 3.35 K Boiling point 3.19 K Triple point 3.05 • 3He: Nuclear spin I = ½, Fermion, Pauli principle. • Superfluid phases: Bose-Einstein condensate of pairs, spins in the liquid state are indistinguishable. • Diamagnetic: levitation under high magnetic field PS) Supersolid state of 3He or 4He? A supersolid is a spatially ordered material with superfluid properties. Superfluidity; a special quantum state of matter, substance is flowing without viscosity. Quantum magnet in triangular angular lattice; breaking translational and rotational symmetry. 3He cooling power Cooling Power proportional to Vapour Pressure L P ∝ exp(− ) RT Latent heat 4He ~90 J/mol Latent heat 3He ~40 J/mol Cooling power: exponentially small at low temperature Pumping on 4He T~1 K (normally down to 1.8 K) Pumping on 3He T~0.26 K (down to 0.3 K) 3He Refrigerator • Sample in vacuum configuration, only few places operate sample in liquid 3He • Operation one-shot mode: keep base temperature 10-60 hours continuous mode: forever? ~very long time • 3He is stored in a sealed space (closed system) to avoid loss, keep low pressure (<1atm) • 3He pump: sealed (tight, casted) pump or charcoal pump One-shot mode Continuous mode Pumping Pumping (gas) (gas) 1 K 3He Refrigerator operation Reach 0.3 K base temp: Clean gas => Make liquid 3He => Reduce pressure Needle valve 1K pot pumping 4 pumping condensing Sample space 3He operation 1) Cleaning gas through LN 2 trap or use cryopump 2) Condense by heat exchange with 1 K pot 3) Cool condensate to 1.5 K (below 2 K) 4) Start pumping to reach 1 base temperature 1K 2 pot 3He 3 pot 3He Storage LN 2 trap cleaning gas 3He Refrigerator operation: closed system Charcoal Charcoal is a light black residue consisting of carbon and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Cryopumps are often combined with sorption pumps by coating the cold head with highly adsorbing materials such as activated charcoal or a zeolite. As the sorbent saturates, the effectiveness of a sorption pump decreases, but can be recharged by heating the zeolite material (preferably under conditions of low pressure) to outgas it. The breakdown temperature of the zeolite material’s porous structure may limit the maximum temperature that it may be heated to for regeneration. from Wikipedia Activate ~ 40 K, control with heater and thermometer 3He Refrigerator operation: closed system Needle valve 1K pot pumping 3He operation 3He gas storage 1)Cleaning gas cryopump (charcoal) – at 4 K all gases inside charcoal sorption pump 2)Release gas by heating up to 40 K 3)Condense by heat exchange with 1 K pot Sample 4)Cool condensate to 1.5 K (below 2 K) in space He-3 pot 5)Start pumping to reach base temperature using sorption pump-set 4 K Charcoal Sorption pump 1K pot 3He pot 3He Refrigerator operation: closed system 3He storage vessel 1 2 3 4 K 40 K 4 K Charcoal Sorption pump 1K pot 3He pot 3He Refrigerator operation: sample in liquid Top loading: measurements inside 3He liquid ) Sample holder O-ring seal Vacuum line Knife gate valve (KF) 3He gas handling system vacuum Rotator Electrical transport 3 4 Resistivity He He 300 kHz 50 µA, 500 µA ? 3He thermometer 10 10 8 ) 6 Ω at 14 Tesla: 0.14 K shift 4 1 (k R 2 ) Ω H = 0 0.4 0.6 0.8 1.0 1 T 3 T T R (k (K) 5 T 7 T 0.1 9 T 14 T 1 10 100 T (K) Cernox CX-1030 - negative magnetoresistance (MR) < 10 K MR effect can be ignored T > 30 K Below 0.3 K ? Cooling Power proportional to Vapour Pressure L P ∝ exp(− ) RT How cool below 0.2 K? How can exponentially small vapor pressure be overcome? Oxford dil 3He and 4He Mixture The working fluid mixture of the dilution refrigerator: phase separation into 3He rich (concentrated) and 3He poor (dilute) phase below 800 mK (NOT PURE 3He and 4He).